No abstract

Here, we report the synthesis and characterization of a hydrogel based on ethylene glycol diglycidyl ether (EGDE) and 1,8-diamino-3,6-dioxaoctane (DA). Chemically stable Co(II) and Cu(II) coordination complexes were prepared with this nonsoluble polyelectrolyte, poly(EGDE-DA), and studied by ss-NMR, FT-IR, thermogravimetry, and microscopy. Mesopores were found in all the samples, the thermal stability of the polymer matrix was highly affected by the presence of metal ions, and the (13)C CP-MAS spectrum for the Cu(II)-complex evidenced a significant increase in the reticulation degree by Cu(II) ions. The catalytic activity of these materials on H2O2 activation was studied by electron spin resonance (ESR). The Co(II)-poly(EGDE-DA)/H2O2 heterogeneous system produced O2, an anion superoxide (O2(•)¯), and a hydroxyl radical (OH(•)), which diffused into the solution at the time that a decrease in pH was detected. In the same way, the Cu(II)-poly(EGDE-DA)/H2O2 heterogeneous system produced O2 and OH(•). H2O2 activation by the poly(EGDE-DA) complexes with Co(II) and Cu(II) were applied on the decolorization of solutions of the azo-dye methyl orange (MO). In the presence of 63 mM H2O2, 87% of MO was removed in 10 min with Cu(II)-poly(EGDE-DA) and in 110 min with Co(II)-poly(EGDE-DA). In addition, the pharmaceutical product epinephrine was partially oxidized to adrenochrome by the O2(•)¯ released from the Co(II)-poly(EGDE-DA)/H2O2 heterogeneous system.

We report the performance of Co­(II) and Cu­(II) coordination complexes on H2O2 activation. The heterogeneous catalysts containing aliphatic amine, N-heterocycle, and/or carboxylic acid ligands in hydrogel materials coordinated with Co­(II) or Cu­(II) were used in this study. These complexes were characterized by solid-state NMR, X-ray photoelectron spectroscopy (XPS), and X-ray fluorescence techniques in order to quantify the superficial and bulk metal ion centers together with the aim of elucidating the ligands involved in the uptake of Co and Cu ions. The release of free radicals on H2O2 activation and the identity of reactive oxygen species were studied by spin trapping using DMPO in electron spin resonance (ESR) experiments. The Co­(II) complex/H2O2 systems produced O2, anion superoxide (O2 •–), and hydroxyl radical (OH•), which diffused into the solution at the time that a decrease in pH was detected. A possible catalytic mechanism would involve the Co­(II)/Co­(III) redox couple, according to XPS results. In the same way, the Cu­(II) complex/H2O2 systems produced O2 and OH•, with evidence of Cu­(II)/Cu­(I) redox cycle. For these catalytic systems, there was no direct evidence of intermediary reactive species. The identity of the ligands played a crucial role in the efficiency of catalytic activation. In addition, in the absence of H2O2, the dissolved O2 was activated by most of the complexes tested, releasing only OH•.